1 The effects of the dihydropyridine
calcium channel blocker nifédipine and
the activator Bay K 8644 were investigated in
different behavioural tests involving
dopaminergic systems. These were the
discriminative stimulus induced by amphetamine,
rotational behaviour in rats with unilateral
6-hydroxydopamine (6-OHDA) lesions and
apomorphine-induced yawning in rats.

3 Bay K 8644 (0.06-0.5mgkg-'i-p.) and
nifedipine (5-20mgkg-'i.p.) had no dose-relate
effect on the discrimination performance of rats
trained to discriminate amphetamine from saline.
However, nifedipine dose-dependently reduced the
response rate of amphetamine-treated rats. Bay K
8644 had no effect on this measure except at
high doses that also caused disruption.

5 As the dihydropyridine compounds affected
apomorphine-induced yawning but not penile
erection, and did not affect amphetamine-induced
rotation or drug discrimination, it seems
unlikely that they are affecting dopamine
release in vivo.